the causes of roof fall, their danger level and the benefits of immediate roof support system have been covered

1. IMMEDIATE GROUND
SUPPORT, AFTER
DEVELOPMENT OR STOPE
FACE EXPOSURE, CAN
PREVENT FALLS OF
GROUND.
PRESENTED BY
AQIB ALI NAICH (16MN40)

2. Objectives
• Introduction ·
• Basic face behavior after exposure
• Controllable Parameters
• Mining Engineers support designs
• Primary and Secondary Support
• Products available for prevention of falls of
ground
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3. INTRODUCTION
• Falls of Ground is one of the highest causes of incidents, accidents
and fatal injuries.
• These falls of ground may occur as soon as the face is exposed after
blasting or after machine cutting. The falls of ground can also occur
after support has been installed.
• It is therefore important to support the exposed face as soon as
possible to prevent the falls of ground and to support the face with
the correct support products; and to support the face as designed
and required by the mining engineers.
• The possible reasons for falls of ground, possible support methods
and the products available will be discussed in this presentation.
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4. BASIC FACE BEHAVIOR AFTER EXPOSURE
• Before mining commences, the rock environment is subjected to
stress. The vertical stress is caused by the weight of the overlying
rock, while the horizontal stress is largely unknown.
• These stresses may be generated by plate tectonics. Therefore, the
stresses are generated by the continental plates pushing against one
another.
• When mining exposes the rock face for the first time it does not cause
the stresses, but redistributes the stresses that are already locked in
the rock.
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5. • When roadways and tunnels
or even stopes are created,
there is a concentration of
stresses around the edges
of the excavations.
• This causes the horizontal
stresses in the roof to
magnify, whist the vertical
stresses in the sidewalls are
magnified.
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6. 6

7. CONTROLLABLE PARAMETERS
• To prevent unplanned collapses and falls of ground, the controllable
parameters have to be used in such a way as to counter the negative
stresses and situations.
• The three main controllable parameters are
excavation width,
time of support installation and;
the characteristics of the support system.
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8. • Tunnel/Stope or excavation width: The amount of roof sag is linked
to the width of the excavation. The wider the excavation, the bigger
the possibility of roof sag. The first step to be taken when
encountering bad roof conditions is to decrease the excavation width.
• Time of support installation: The further the rock face advances from
the last line of bolts or support, the greater the unsupported roof
span. As discussed above the greater the roof/road width the greater
the possibility of failure. If a roadway or tunnel is left unsupported for
any length of time, deflection can occur, which causes the roof to
bend and cracks to appear.
• Characteristics of the support system: The support system begins by
identifying the mechanism of roof falls in the area. The second step is
to then design a suitable support system, taking into account the
geological and stress conditions.
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9. MINING ENGINEERS SUPPORT DESIGNS
• Mining Engineering or specifically Rock Engineering is a professional
science that takes many factors into consideration when designing
roof and sidewall support.
• The first step is to determine the load on the system, including gravity
and the presence of horizontal stresses.
• Next, the system has to be able to withstand the imposed loads.
• This is achieved by balancing the length, diameter, spacing of the
proposed support method.
• The load calculation should take into account the loads imposed from
a force point of view, as well as establishing a stable beam.
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10. PRIMARY AND SECONDARY SUPPORT
• Primary support: This is the support that should be installed
immediately after face exposure. Once the face has been exposed,
numerous reactions occur that affect the stability of the roof and
sidewalls.
• Secondary support: After the face has been supported temporally to
protect the workers and allow for the loading of the face, a second
round of long term support is installed.
• This secondary support is only implemented if the condition of the
roof and sidewalls are so poor that additional long term support is
required.
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11. Products available for prevention of falls of ground
• There are numerous products available that could be used to assist the
mine, contractor and engineer to prevent falls of ground.
• Stiff support limits rock movement to the absolute minimum, while soft
support allows movement to take place. Stiff systems also supply constraint
to rock expansion and shearing due to high horizontal stresses.
• Commonly used systems include:
• Mechanical anchor steel tendons
• Friction bolts
• Steel tendon bolts used in conjunction with resin capsules/cement capsules
• Fibre bolts used with resin/cement capsules
• Steel tendons used together with pumpable cement products
• Plastic meshing together with bolts
• Wire mesh and Shotcrete
• Thin sprayed liners, either cement or latex based
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12. CONCLUSION
• As can be learned from the presentation it is very
important to support the face as soon as possible after
exposure.
• There are numerous reasons why falls of ground occur,
but these can be prevented by designing a support
method and pattern, that can assist in the prevention of
falls of ground.
• There are support products on the market that can assist
and prevent these falls of ground, if they are installed
correctly and timelessly
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